1. Field of the Invention
The present invention relates to a radar (apparatus) used in a radar system mounted in a vehicle, in particular, to a so-called multi-beam radar apparatus comprising a plurality of transmitters and receivers.
This application is based on Patent Application No. Hei 11-27598 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, a radar apparatus mounted in a vehicle has been used for detecting an obstacle such as a telegraph/telephone pole or a block fence which is present relatively near the radar apparatus, so as to prevent the vehicle from colliding with the obstacle when parking the vehicle into a garage, or the like. Recently, in addition to such detection for preventing collisions with stationary obstacles, radar apparatuses for performing high speed and highly accurate detection of objects which are relatively far from the radar apparatus have also been developed. This type of radar apparatus is used as a warning system for preventing a running vehicle from colliding with a vehicle ahead of the present vehicle, or as an adaptive cruise control (ACC) system.
The main target of such a radar apparatus is an moving object such as a vehicle running ahead of the present vehicle, or a vehicle approaching the present vehicle. Therefore, the possible detection area is a relatively small angular area in front of the present vehicle. However, the necessary distance to be measured is very wide from a close range such as a few tens of centimeters to a range of a few hundred meters corresponding to a vehicle approaching at a high speed. In consideration of the above requirements, a multi-beam radar has been developed, which has a plurality of transmitting units for emitting thin radar beams and a plurality of receiving units for receiving reflection signals. In this structure, it is possible to cover the necessary angular area as well to obtain the necessary measurement sensitivity over a wide range.
For example, U.S. Pat. No. Re 36,095 of the same applicant of the present application discloses an FM-CW multi-beam radar apparatus whose radar beam is a high-frequency radio-wave beam in the millimeter-wave band. This patent also discloses a time-division radar apparatus having a plurality of transmitting units and receiving units for radiating radar beams having approximately the same radiation pattern in a manner such that a portion of each beam spatially overlaps with each other, and for receiving reflection beams. Here, the detection accuracy is improved by suitably determining each combination and arrangement of the transmitting units and receiving units.
However, such a multi-beam radar apparatus has a specific detection area for each combination of the transmitting unit and receiving unit, and the position of a target object, that is, the azimuth (angle) and the distance of a target vehicle are calculated by synthesizing received data which is obtained for each combination of a transmitting unit and a receiving unit. Therefore, if any one of the transmitting units or receiving units is degraded and has a lower sensitivity, it is necessary to detect the unit concerned.
In consideration of the above circumstances, an objective of the present invention is to provide a multi-beam radar apparatus having a plurality of transmitting units and receiving units, in which an abnormal state of a transmitting or receiving unit due to degradation, problems, or the like, can be detected, thereby preventing problems due to degradation of the sensitivity or the like.
Therefore, the present invention provides a radar apparatus comprising:
a transmitting section including a plurality of beam transmitting units for radiating a plurality of beams, where adjacent beams have an overlapped portion; and
a receiving section including a plurality of beam receiving units for receiving reflection waves reflected from a target object,
wherein transmitting and receiving combinations between the beam transmitting units and the beam receiving units are determined so as to detect the position of the target object, and
the radar apparatus further comprises:
a sensitivity comparing section for comparing sensitivities with respect to the transmitting and receiving combinations; and
an abnormal state determination section for determining an abnormal state of any one of the beam transmitting units and the beam receiving units based on a result of the comparison of the sensitivity comparing section.
Typically, the beam transmitting units respectively correspond to the beam receiving units as transmitting/receiving channels, and the transmitting and receiving combinations are determined in each channel and also between adjacent channels; and the sensitivity comparing section compares sensitivities with respect to the combination of each channel, and also compares sensitivities with respect to the combination of each pair of the adjacent channels.
According to the above structure, it is possible to detect the sensitivity with respect to each combination of the transmitting and receiving units. Here, the sensitivity of each combination of the corresponding transmitting and receiving units of the same channel, that is, with respect to each radiated radar beam, is called the individual sensitivity. In contrast, the sensitivity of each combination of the transmitting and receiving units belonging to the adjacent channels is called the adjacent sensitivity. In the latter case, a radar beam is radiated from a beam transmitting unit, and the relevant reflection wave is received by a beam receiving unit belonging to the adjacent channel; thus, the adjacent sensitivity relates to the overlapped portion of the beam radiation patterns of the two channels. By comparing the individual sensitivities with each other, and also by comparing the adjacent sensitivities with each other, an abnormal state such as the sensitivity degradation of any one of the beam transmitting and receiving units can be determined in a uniform environment.
The above radar apparatus may further comprise a transmitting and receiving channel switching section for switching the transmitting and receiving channels of a transmitting and receiving combination between the adjacent channels in a manner such that the channel of the beam sending unit and the channel of the beam receiving unit are replaced with each other.
In this case, (i) the adjacent sensitivity detected when a radar beam transmitted from the transmitting unit of a channel (here, called the first channel) and the relevant reflection wave is received by the beam receiving unit of the adjacent channel (here, called the second channel) and (ii) the adjacent sensitivity detected when a radar beam transmitted from the transmitting unit of the second channel and the relevant reflection wave is received by the beam receiving unit of the first channel can be compared. That is, a plurality of adjacent sensitivities with respect to the same area in a spatially overlapped portion of the radar beams can be detected, and the adjacent sensitivities as well as the individual sensitivities can be respectively compared. Therefore, any one of the beam transmitting and receiving units in an abnormal state, such as sensitivity degradation, can be specified regardless of the state of the target vehicle, that is, in either of the running or stopped state.
If a radar system using the radar apparatus having the above structure is constructed, any one of the beam transmitting and receiving units in an abnormal state such as the sensitivity degradation can be specified and a warning display can be shown on the instrument panel of the present vehicle. Accordingly, the driver or a passenger can be informed of the abnormal state of the radar apparatus and a problem due to the abnormal state can be prevented.
If the abnormal state determination section determines degradation (such as sensitivity degradation or a problem) in any one of the beam transmitting units and the beam receiving units, the radar apparatus preferably further comprises a degradation correcting section for correcting the degradation of the target unit based on the determination of the abnormal state determination section.
For example, the relevant beam transmitting or receiving unit which is determined by the abnormal state determination section to have a lowered sensitivity, or a detected value obtained by the relevant unit in the abnormal state, can be efficiently corrected according to the level of the sensitivity degradation.
Therefore, if it is determined that any one of the beam transmitting units and the beam receiving units has been degraded and thus has a lower sensitivity, the driver or a passenger can be informed of the sensitivity degradation by means of the above warning display or the like, and simultaneously, the degraded sensitivity characteristic can be corrected by the degradation correcting section, thereby normally operating the radar apparatus and the radar system using this radar apparatus.